LIQUID-PHASE PROPERTIES AND SPARGER DESIGN EFFECTS IN AN EXTERNAL-LOOP AIRLIFT REACTOR

A synergistic effect of liquid-phase properties and sparger design on the performance of an external-loop airlift reactor was observed in ou r experiments. The absolute changes of gas holdup reflecting the varia tions of gas dispersion mode and system properties were, however, less pronounced than in the bubble column reactors due to the equalizing e ffect of induced liquid circulation on the riser hydrodynamics. The to tal increase of gas holdup observed in aqueous solutions of inorganic salts was independent of the type of salt and varied only with the gas dispersion mode. For all electrolytes studied, the respective limitin g dependence E vs u(G) were obtained at concentrations close to the tr ansition coalescence concentrations of individual electrolytes, while Further increase of salt concentration had a negligible effect on gas holdup values. The Zuber and Findlay drift flux model fitted well the data of riser gas holdup for the heterogeneous bubbling conditions; it , however, failed to reflect the transition between the heterogeneous and homogeneous bubbling regimes. Data for the homogeneous bubbling re gime were adequately described by the slip velocity concept when the f unctional relation between slip velocity and riser gas holdup was expr essed by the modified equation of Davidson and Harrison.